I have a 7.4 L fuel injected V8, currently running Starbrite semi-synthetic 25w-40 (because it was cheap at Walmart). My next change will be Triax full synthetic Marine Ultra 25w-40. It's the best deal around at $38 for 5 quarts. I am currently running Triax marine gear lube in the gearcase, Triax fluid in the power trim, and power steering unit as well. Love this stuff.